Fifteen percent of classic hemophiliacs develop an antibody (inhibitor) to exogenous factor VIII that seriously hampers their health, increases the cost of their care over 4-fold to $32,000/patient/year, and drains valuable blood resources by divering source plasma from other uses. Accurate prediction of inhibitor development in hemophiliacs would enable use of interventional methods to alter the antibody (immune) response in such patients. Since gene deletions have been shown to occur in growth hormone-deficient children who develop antibody to exogenous growth hormone and since factor IX hemophiliacs with inhibitor also have gene deletions, analysis of factor VII gene defect(s) may be relevant to inhibitor formation. This project will adopt a stepwise strategy to characterize gene alterations useful in predicting inhibitor development among hemophiliacs. Using 32P-labeled genomic probes specific for exons from the human factor VIII gene, this project will screen by Southern blot analysis leukocyte DNA from 60 hemophiliacs with inhibitor and 180 without inhibitor for mutations at known TaqI restriction sites within factor VIII exons. Five of seven such TaqI sites could give rise to stop codons if C yield T substitutions have occurred. If the inhibitor patient cohort has no specific TaqI site alterations to discriminate them from the non-inhibitor cohort, the project will then use these probes to study a panel of restriction endonucleases, including EcoRI, BamHI, SstI, and 7 other endonucleases chosen on the basis of known fragment sizes from the factor VIII gene restriction map. Each of the ten different digests from each patient will be studied using a variety of factor VIII exon probes to detect small gene deletions or insertions recognizable by their production of novel fragments not seen in controls. Inhibitor-patient specific gene alterations will be studied utilizing the appropriate enzyme and probe to prospectively screen all newly-diagnosed hemophiliacs in the southeast region. If no inhibitor-patient specific gene alterations are detected by these methods, we will compare the distributions of patient and control haplotypes derived from known restriction fragment length polymorphisms and any new polymorphisms observed in this project. Comparison of haplotype differences may predict gene alterations specific for inhibitor patients that could be used to prospectively screen all hemophiliacs to predict inhibitor development and to determine the relative contributions of specific factor VIII gene alterations in the two hemophiliac populations.